Effect of Processing Parameters on Superplastic and Corrosion Behavior of Aluminum Alloy Friction Stir Processed

Abstract

Friction Stir Processing (FSP) is a variant of Friction Stir Welding, and can be used to modify the materials microstructure to functionalize it. Superplastic forming is a technological process used to produce components with very complex shapes. In the last two decades it has been a topic of major development. In Fine Structure Superplasticity (FSSP), the initial grain size exerts a strong influence on the superplastic strain rate and temperatures. Refining grain size (GS) the parameters (temperature and strain rate) of superplastic forming could be optimized. Thermal stability is also an important factor to obtain superplasticity. FSP is used to refine GS, but the optimum processing parameters are still under study over different materials. Corrosion resistance can be affected by FSP too, but the information about it is scarce. In the present study, 7075-T651 aluminium alloy was friction stir processed under different conditions in order to improve superplastic behavior. Tool profile, rotation rate and traverse speed were analyzed. Microstructures with <4 μm grain size were obtained. The maximum superplastic elongations, in a range of 740 to 900%, at 400°C were obtained at 1x10-2s-1strain rate. The results were discussed in terms of constitutive equations and microstructure evolution. Localized corrosion potentials were obtained. Localized corrosion resistance was affected by friction stir processing.